ESO astronomers have used the Very Large Telescope’s (VLT) Multi Unit Spectroscopic Explorer (MUSE) instrument to make detailed observations of a cosmic collision, revealing secrets as to how star-forming gas was ripped out of a distant spiral galaxy. The findings help shed light on the mystery of how star formation ceases in galaxy clusters.

The team made use of MUSE – a new, visible wavelength instrument designed for the discovery of objects that standard imaging surveys aren’t able to identify. MUSE provides astronomers with a band of colors (or spectrum) for every pixel recorded, allowing them to build a detailed map of the properties and motions of the objects being studied.

The instrument was used to study the spiral galaxy ESO 137-001 as it moves into the Norma Cluster. The spiral galaxy, located 200 million light-years away, is undergoing a process known as ram-pressure stripping, wherein a strong drag force is exerted upon the object, eroding its raw materials.

Falling into a cloud of thin, hot gas at a speed of several million kilometers per hour, ESO 137-001 is being stripped of the majority of the gas required to produce young stars, transforming it from a blue galaxy – filled with the gas required for star-formation – into a gas-poor red one.

MUSE has allowed the team to not only confirm the existence of the gas in and around the galaxy, but also to observe how it moves. Viewing the object for a single hour was enough to build a high-resolution image detailing the distribution and movement of material in the object. The team found that the gas had already been fully stripped from the outer edges of the galaxy, where the gravity from less dense star clusters has a weaker hold on the material.

"It is one of the major tasks of modern astronomy to find out how and why galaxies in clusters evolve from blue to red over a very short period of time," said Durham University’s Michele Fumagalli, the team lead on the project. "Catching a galaxy right when it switches from one to the other allows us to investigate how this happens."

Eventually, all galactic gas will be swept out into bright streaks behind the galaxy, stretching out over 200,000 light-years. Both the gas in the bright tails and stars in ESO 137-001 continue to rotate in the same way, providing further evidence that it is the gas in the cluster, rather than gravity, that’s responsible for the stripping.